Oaks, member of the genus Quercus, are some of the best known trees in the world, with over 500 species found all over the northern hemisphere. Leaves are usually lobed, sometimes evergreen, and the fruit is a nut called an acorn. The wood is prized for carpentry, and the bark has been used for medicinal purposes because of its high tannin content. Their fine fall color and deep, non-invasive roots make them valued garden ornamentals.
Oaks with evergreen leaves are commonly called "live oaks," though many are fully or partially deciduous in colder areas. Probably the best known is the Southern Live Oak (Q. virginiana), native to the southeastern United States. Others native to North America include the Coast Live Oak (Q. agrifolia) and the Emory Oak (Q. emoryi). Both the the Holly Oak (Q. ilex) and the Cork Oak (Q. suber) are native to the Mediterranean. The Japanese Live Oak (Q. myrsinifolia) is native to China and Japan.
White oaks tend to have smoother, lighter colored bark than red oaks and lighter wood. Their acorns are generally sweet, containing little tannin and ripen in a single year.
These include the White Oak (Q. alba), the Swamp White Oak (Q. bicolor), the Rocky Mountain White Oak (Q. gambeli), the Garry Oak or Oregon White Oak (Q. garryana), the California White Oak (Q. lobata) and the Bur Oak (Q. macrocarpa). All these are North American trees.
The English Oak (Q. robur) is native to Europe and Asia Minor and is known for its longevity--some trees are known to be 800 to 1000 years old--as well as its beautiful spreading form.
Red And Black Oaks
The red and black oaks are native to Central and North America and have dark bark, often furrowed, and reddish brown wood. The acorns are bitter, high in tannins and usually take two years to ripen.
These include the Scarlet Oak (Q. coccinea), the Southern Red Oak (Q. falcata), the Red Oak (Q. rubra), the Shumard Red Oak (Q. shumardii), the Water Oak (Q. nigra), the Black Oak (Q. kelloggii) and the Pin Oak (Q. palustris).